After years of being annoyed by these kinds of unfriendly unsubscribe policies, I now use disposable e-mail addresses to sign up for most web-based services. These have two advantages: (1) If they refuse to unsubscribe you, you can disable the address and never hear from them again; (2) If your e-mail address gets leaked to spammers, you know who did it, since you provide a unique address to every service. (I still use my real e-mail address with critical services such as on-line banking.)

I've been very happy with the disposable e-mail provided by http://spamgourmet.com; it's free, reliable, and you can create a new disposable address without visiting their web site. (It's not a pretty-looking web site, but it does the job.)